Despite the inevitability of aging and the importance of vision to individual well being, the visual changes that occur in older persons are poorly understood. The major goal of this application is to better equip the author to contribute significantly to the more basic aspects of this important but neglected area of visual science. The aims of the proposed research are to discover the extent to which aging alters the basic processes of lateral inhibition and visual channel function, to determine the impact of such changes on visual function and to evaluate a proposed "transient/sustained shift" hypothesis of visual aging. The studies in Part I are designed to: (1) determine if an age-related "shift" from "transient" to "sustained" channel functioning can explain losses in temporal resolution, spatial discrimination and response speed and relatedly, (2) to model visual aging through selective desensitization of the different visual channels by manipulation of the stimulus parameters to which they are differentially sensitive (e.g., spatial frequency, drift rate, flicker). In Part II the effects of age on the fundamental process of lateral inhibition will be determined by an age comparison of: (1) the luminance compensation required to offset lateral inhibition-induced simultaneous contrast effects, (2) the strength of Mach bands using Von Bekesy's compensation technique, (3) the temporal development of Craik/O'Brien contour enhancement using a novel peripheral masking procedure and (4) the strength of the Craik/O'Brien effect using a specially developed contour-based brightness matching procedure. The long-term objectives of this proposal are to advance our understanding of the effects of aging on basic visual processes, to expand the data base for the development of effective age-appropriate visual tests and to develop a broad and systematic theory to guide future research into visual aging.